Abstract
Chemotactic responses of Dictyostelium discoideum cells to periodic self-generated signals of extracellular cAMP comprise a large number of intricate morphological changes on different length scales. Here, we scrutinized chemotaxis of single Dictyostelium discoideum cells under conditions of starvation using a variety of optical, electrical and acoustic methods. Amebas were seeded on gold electrodes displaying impedance oscillations that were simultaneously analyzed by optical video microscopy to relate synchronous changes in cell density, morphology, and distance from the surface to the transient impedance signal. We found that starved amebas periodically reduce their overall distance from the surface producing a larger impedance and higher total fluorescence intensity in total internal reflection fluorescence microscopy. Therefore, we propose that the dominant sources of the observed impedance oscillations observed on electric cell-substrate impedance sensing electrodes are periodic changes of the overall cell-substrate distance of a cell. These synchronous changes of the cell-electrode distance were also observed in the oscillating signal of acoustic resonators covered with amebas. We also found that periodic cell-cell aggregation into transient clusters correlates with changes in the cell-substrate distance and might also contribute to the impedance signal. It turned out that cell-cell contacts as well as cell-substrate contacts form synchronously during chemotaxis of Dictyostelium discoideum cells.
Highlights
Dictyostelium discoideum (D. discoideum) is a life form that proliferates as single amebas and when starved, aggregates into a mound of approximately 105 cells that eventually turns into a migrating slug, which further differentiates into a fruiting body to facilitate spore dispersal
The primary goal of this study was to elucidate the origin of impedance oscillations generated by starved D. discoideum amebas that have been cultured on small gold electrodes
We speculated that these impedance oscillations might be attributed to synchronous shape changes of amebas similar to what is inferred from optical density oscillations [33]
Summary
Dictyostelium discoideum (D. discoideum) is a life form that proliferates as single amebas and when starved, aggregates into a mound of approximately 105 cells that eventually turns into a migrating slug, which further differentiates into a fruiting body to facilitate spore dispersal. Individual cells, which are able to detect a discrepancy of as much as 5 occupied receptors between front and back of the cell body, migrate into the direction of increasing cAMP concentration producing spatiotemporal waves that can be visualized by dark-field microscopy [19,20]. These variations in light scattering properties are believed to originate from cell shape or cell density changes that occur during the chemotactic cycle producing time periods of 5–6 minutes [10,21]. Cellsubstrate contacts of small ensembles in 2-D during chemotaxis have yet to be studied
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